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TROUBLESHOOTING
The check engine lamp on was discussed in the previous page with the exception of problems can can occur such as "no ses lamp", "no aldl data or won't flash code 12, light stays on." We'll overview these two problems:
No "Service Engine Soon" lamp: There should always be a steady "ses" lamp with the ignition key in the "on" position, and the engine not running. Power to to the lamp is supplied through the pnk/blk wire is energized through the ignition switch (+12V), the ecm controls the lamp (brn/wht wire) by grounding it internally in the ecm control circuit through ecm terminal A5. Using your test lamp connected to a hot wire, probe the system ground wires to be sure you have a good ground. Connect your test lamp to ground, and probe the pnk/blk wire to make sure power is present. If you have a terminal "D" on your aldl terminal, connect a jumper wire from a hot and touch this terminal "D" only. The lamp should come on. If not, replace bulb.
If you have checked the bulb, wiring and connections, and still have no "ses" lamp, the ecm is at fault. But be sure to thoroughly check all the wiring and terminals, before you replace the ecm.
No ALDL data, won't flash code 12, light on steady: This is usually caused by a shorted (brn/wht) wire to ground, or a open wire in the ALDL terminal "A" to ecm pin A9, when the terminals "A" and "B" are connected for a diagnostic check. First try unplugging the A-B ecm connector, if the light goes off, then the brn/wht wire is not shorted to ground, and the wht/blk wire from the ALDL to ecm is not opened. Check all terminal connectors. If they check out, the problem is a faulty memcal, or ecm. If a code did not flash, the ecm should be replace using the original memcal. Replace the memcal only if a ecm swap did not correct the problem.
Engine cranks but won't run: Be sure the battery voltage is sufficient (around 12.5 volts + or - .5V or so), the starter cranking speed is sufficient to turn the engine over with no hesitation, and their is fuel in the tank. Jumper the ALDL terminals "A" and "B", with ignition switch on, but engine not running, see if you have code 54. If you do, check the wiring to the fuel pump relay. Pull your ALDL jumper, turn the ignition key off for about 15 seconds, then to "on" position again. You should hear the fuel pump run for about two seconds, and then stop. If this does not happen, locate the fuel pump test terminal "G" on the ALDL, connect a jumper from a hot wire source, and connect to this terminal. The fuel pump should run. If it does, the fault is in the relay, or the ecm. If the pump does not run, check the connection of the fuel pump by the fuel tank for a loose or corroded connection. Circuit below is what is typical with a 1985-89 tpi harness with maf sensor.
If you are using a 1988 and later ecm and do not have a VATS encoder module OR the VATS has not been removed from the prom, you will have to correct this problem first.
Once you are satisfied the fuel pump is good and the engine still won't start, you'll need to see if you have secondary voltage at the ignition coil. For either a internal coil (large cap) HEI, or a small cap (external coil), check to make sure you have 12 power on the pink wire that supplies power to the ignition coil. Also be sure there is a good ground especially if you are using the remote coil, as it needs a solid ground to mount the coil frame. For the large cap HEI, pull one of the spark plug wires, or if you have a remote coil, pull either the coil wire or spark plug wire and put it close to a metal bracket (unpainted), or even a exhaust manifold bolt, be sure not to get your fingers close to the spark plug end of boot. With a remote starter button, or a assistant to turn the ignition key to crank engine, see if you have spark at the wire jumping to the metal surface. If not check the coil for an open (you'll need a automotive manual to show you how to hook up a ohmmeter to check for resistance and opens), if the coil is bad, replace coil. if the coil checks good, the next item to check is the ignition module. This where a sensor tester comes in handy, using the instructions, hook up the tester to the module according to the steps outlined. If you don't have the tester, many automotive stores have testers, and most will test it for free. If the ignition module is bad, replace it. If it checks out okay, if the ecm is activating the injectors.
The noid lights shown above. The noid light on the left is for tpi systems, the one on the right is for GM TBI systems.
Disconnect on of the injectors from the harness, and with a injector tester lamp (noid lamp), or a test lamp that one end is connected to a hot (12V), probe the green/blk or blue/black wire and with the engine cranking, the lamp should blink. If it blinking, the problem lies in the fuel delivery system, that will be discussed a little later. If the light is steady, the problem is in the injector drive circuits, the green/blk or blue/black wires that are shorted somewhere to ground. You'll have to pull the terminal to the ecm and with all the injectors disconnected, hook up your continuity tester to ground and probe these wires, the light should not come on. If it does, find and repair the shorted wires. If the lamp does not come on, check the resistance of each injector, with your ohmmeter, the resistance should be more than 10 ohms( typically around 15-16 ohms). If the injectors check out okay, the ecm is faulty. If the not okay, replace the any injectors that measure less than 15 ohms. Now, if you don't have a blinking light, plug in the injectors back in, then you'll need to turn the ignition key on and probe the injector harness terminals to ground with your test lamp, the light should be on at both terminals, this is due to the fact the injectors are wired in parallel. If there is not a light at both terminals, the problem is in the injector harness. If the light comes on one wire, the problem is in the harness to the injectors.
Now, if the light comes on in both terminals, reconnect your test light to injector harness, and disconnect the 4 way distributor connector. Momentarily touch the connector with the purple/white wire with a test light hooked to 12V, if the injector light blinks the problem is a bad ignition module. If there is no blinking light, disconnect the tps and repeat the test. If the light blinks, replace tps. No blinking light means you'll need to make sure the fuel pump runs for its two second priming period. If the fuel pump checks out okay, reconnect all your injectors, turn the ignition off, disconnect your ecm, turn the ignition key back on, and probe terminal D15 with the test light connected to a hot power source, if the light comes on, you'll need to wires to injectors (green/blk or blue/black) being shorted to a voltage source. If they are okay, the ecm is at fault.
click here to go to SES and Engine will not run troubleshooting flow charts
Now, if fuel pump did not come on, you'll need to check for open or grounded ppl/white wire to the distributor 4-way connector back to ecm terminal B5.Also check for open wires to injector harness, green/blk or blue/black wires.
click here to go to fuel pump relay and fuel system problem flow charts.
